CAST AI Rate Limits Skill

CAST AI Rate Limits

Overview

The CAST AI REST API enforces rate limits per API key. The autoscaler agent communicates cluster state at 15-second intervals. For custom API integrations, implement exponential backoff and request queuing to avoid hitting limits.

Prerequisites

CAST AI API key configured
Understanding of the API endpoints you call

Rate Limit Behavior

| Aspect | Value | |--------|-------| | Rate limit scope | Per API key | | Response on limit | HTTP 429 with Retry-After header | | Agent sync interval | Every 15 seconds | | Recommended polling | No more than once per 30 seconds |

Instructions

Step 1: Detect Rate Limits from Response Headers

async function castaiRequest(path: string): Promise<Response> {
  const response = await fetch(`https://api.cast.ai${path}`, {
    headers: { "X-API-Key": process.env.CASTAI_API_KEY! },
  });

  // Log rate limit headers for monitoring
  const remaining = response.headers.get("X-RateLimit-Remaining");
  const reset = response.headers.get("X-RateLimit-Reset");
  if (remaining) {
    console.log(`Rate limit remaining: ${remaining}, resets: ${reset}`);
  }

  if (response.status === 429) {
    const retryAfter = parseInt(response.headers.get("Retry-After") ?? "5");
    throw new RateLimitError(retryAfter);
  }

  return response;
}

class RateLimitError extends Error {
  constructor(public retryAfterSeconds: number) {
    super(`Rate limited. Retry after ${retryAfterSeconds}s`);
  }
}

Step 2: Exponential Backoff with Jitter

async function withBackoff<T>(
  fn: () => Promise<T>,
  maxRetries = 5
): Promise<T> {
  for (let attempt = 0; attempt <= maxRetries; attempt++) {
    try {
      return await fn();
    } catch (err) {
      if (attempt === maxRetries) throw err;

      let delayMs: number;
      if (err instanceof RateLimitError) {
        delayMs = err.retryAfterSeconds * 1000;
      } else {
        delayMs = Math.min(1000 * Math.pow(2, attempt), 30000);
      }
      // Add jitter to prevent thundering herd
      delayMs += Math.random() * 1000;

      console.log(`Retry ${attempt + 1}/${maxRetries} in ${delayMs}ms`);
      await new Promise((r) => setTimeout(r, delayMs));
    }
  }
  throw new Error("Unreachable");
}

Step 3: Request Queue for Batch Operations

import PQueue from "p-queue";

// Limit concurrent requests and enforce interval
const castaiQueue = new PQueue({
  concurrency: 3,
  interval: 1000,
  intervalCap: 5,   // Max 5 requests per second
});

async function queuedCastAIRequest<T>(fn: () => Promise<T>): Promise<T> {
  return castaiQueue.add(() => withBackoff(fn));
}

// Batch process multiple clusters
const clusterIds = ["id1", "id2", "id3", "id4", "id5"];
const savings = await Promise.all(
  clusterIds.map((id) =>
    queuedCastAIRequest(() =>
      fetch(`https://api.cast.ai/v1/kubernetes/clusters/${id}/savings`, {
        headers: { "X-API-Key": process.env.CASTAI_API_KEY! },
      }).then((r) => r.json())
    )
  )
);

Step 4: Polling Best Practice

// Do NOT poll faster than 30 seconds for cluster state
// The agent syncs every 15s; polling faster adds no value

async function pollClusterStatus(
  clusterId: string,
  intervalMs = 30000
): Promise<void> {
  const timer = setInterval(async () => {
    try {
      const status = await queuedCastAIRequest(() =>
        fetch(
          `https://api.cast.ai/v1/kubernetes/external-clusters/${clusterId}`,
          { headers: { "X-API-Key": process.env.CASTAI_API_KEY! } }
        ).then((r) => r.json())
      );
      console.log(`Cluster ${clusterId}: ${status.agentStatus}`);
    } catch (err) {
      console.error("Poll failed:", err);
    }
  }, intervalMs);
}

Error Handling

| Scenario | Detection | Response | |----------|-----------|----------| | 429 with Retry-After | Check header | Wait exact duration | | 429 without header | Status code only | Exponential backoff from 1s | | 5xx errors | Status >= 500 | Retry up to 3 times | | Connection timeout | Fetch throws | Retry with longer timeout |

Resources

CAST AI API Reference
p-queue -- concurrent request queue

Next Steps

For security configuration, see castai-security-basics.

Agent Skills: CAST AI Rate Limits

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